1. Field of the Invention
The present invention relates to methods and apparatuses for reading identification marks indicating wafer numbers and lot numbers formed on surfaces of wafers.
The present application claims priority on Japanese Patent Application No. 2007-168303, Japanese Patent Application No. 2007-168304, and Japanese Patent Application No. 2007-168305, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In factories and manufacturing sites for manufacturing semiconductor devices, multiple wafers (bundled into manufacturing lots) stored in cases are transported between multiple processes in manufacturing. Plenty of processes have been performed on wafers; hence, each wafer displays an identification mark representative of a device type, a model number, a lot number, and a wafer number, thus avoiding wafers from being erroneously identified due to complex processes.
Conventionally, laser markers are used to form identification marks on wafers, wherein marking dots are collectively formed so as to indicate prescribed numbers and characters. Identification marks can be formed on the backsides of wafers, wherein swelling portions may occur on the surfaces of wafers when the backsides of wafers are subjected to vacuum absorption for the purpose of transportation and the like. This may cause defocusing in photolithography and polish failures in chemical mechanical polishing (CMP). For this reason, identification marks have been normally formed on the surfaces of wafers.
In order to specify wafers or lots in manufacturing, identification marks have been recognized by reading apparatuses equipped with CCD cameras, for example. Some reading apparatuses for reading identification marks have been equipped with transport robots for transporting wafers to cases. This makes it possible to sort or align wafers (specified by reading apparatuses) in ascending or descending orders of numbers of identification marks into cases. This technology has been disclosed in various documents such as Patent Document 1, which teaches a physical distribution system of wafers.    Patent Document 1: Japanese Unexamined Patent Application Publication No. H05-147723
The aforementioned reading apparatus for reading identification marks formed on wafers suffer from problems in that, when the surfaces of wafers are sealed with resins covering identification marks, it is difficult to recognize the identification marks. In the manufacturing of semiconductor devices, there are provided wafers on which multiple integrated circuits (ICs) are formed on surfaces, wherein re-wirings are formed to establish electric connections between pad electrodes and integrated circuits, pillar electrode terminals (or metal posts) composed of copper are formed on re-wirings, and then the surfaces of wafers are sealed with resins. Before integrated circuits, re-wirings, and metal posts are sealed with resins, it is possible for human operators to visually recognize identification marks formed on the surfaces of wafers; however, after sealing, identification marks are completely sealed with resins; hence, it is impossible to visually specify wafer numbers and lot numbers.
Identification marks may be read before or after the dicing of wafers in manufacturing, wherein dicing tapes are adhered to the backsides of wafers, which makes it more difficult to read the identification marks.